Method and machine for truing grinding wheels



July 6, 1943. G. F. JOHNSON METHOD AND MACHINE FOR TRUING GRINDING WHEELS Filed Sept. 15, 1941 4 Sheets-Sheet 1 G. F. JOHNSON July 6, 1943.

METHOD AND MACHINE FOR TRUING GRINDING WHEELS Filed Sept. 15,

1941 4 Sheets-Sheet 2 METHOD AND MACHINE FOR TRUING GRINDING WHEELS Filed Sept. 15, 1941 4 Sheets-Sheet 3 61- [6 66 1 a 3 68 63A) 6/? J Jf/J ap July 6, 1943. JQHNSQN 2,323,401

METHOD AND MACHINE FOR TRUING GRINDING WHEELS Filed Sept. 15, 1941 4 Sheets-Sheet 4 K 115 47 v i 147 19?? ERIN F Lf b 50 Patented July 6, 1943 METHOD AND MACHINE FOR TRUING GRINDING WHEELS Glen F. Johnson, Detroit, Mich., assignor to Bower Roller Bearing Company, Detroit, Mich, a corporation of Michigan Original application December 23, 1940, Serial No.

Divided and this application September 15, 1941, Serial No. 410,818

2 Claims.

Th s invention relates to abrading methods and apparatus and in particular to such method and apparatus for truing the abrading wheels used therein.

One object is to provide mechanism for and a method of truing a grinding wheel for substantially simultaneously grinding the raceway and one side wall and one edge of an anti-friction bearing cone.

Another object is to provide mechanism for and a method of truing a grinding Wheel consisting in forming a peripheral groove in the grinding wheel having wall portions arranged for simultaneously grinding a side wall and rounding the outer edge of the side wall to a predetermined curvature.

Another object is to provide mechanism and a method of truing a grinding Wheel consisting in forming an annular peripheral portion on the grinding wheel inclined to the axis of rotation thereof for grinding a bearing raceway, and forming an annular groove with a rounded bottom adjacent said annular portion adapted to grind a side wall of the bearing race adjacent the raceway and at the same time to round the outer edge thereof.

This application is a division of my co-pending application Serial No. 371,297, filed Dec. 23, 1940, for Grinding machine and method.

In the drawings:

Figure 1 is a top plan view, partly in section, of a preferred embodiment of a machine for simultaneously grinding the raceway, one side wall and an edge of an anti-friction bearing cone, together with mechanism for truing the grinding wheel to the desired configuration, with the parts in position for grinding the bearing cone.

Figure 2 is a position similar to Figure l but with the parts in position for truing the grinding wheel.

Figure 3 is a vertical section along the line 3-3 in Figure 1 through the work support.

Figure 4 is a vertical longitudinal section along the line i4 in Figure 1, through the grinding wheel truing mechanism.

Figure 5 is a vertical cross section along the line 55 in Figure 1, through the grinding wheel truing mechanism.

Figure 6 is a horizontal section along the line 66 in Figure 5.

Figure 7v is a fragmentary side elevation of the end of the grinding wheel truing mechanism, looking in the direction of the arrows 1-1 in Figure 6.

Figure 8 is a view similar to Figure 7 but at right angles thereto, looking in the direction of the arrows 88 in Figure 6.

Figure 9 is an enlarged fragmentary horizontal section of the groove truing diamond shown in Figure 6 with the diamond at the end of the operation.

Figure 10 is a horizontal view of the face truing diamond during the operation of truing the face 01 the grinding wheel.

Figure 11 is an enlarged horizontal section of the central portion of Figure 1, showing the raceway, one side wall, and an edge of an anti-friction bearing cone being simultaneously or concurrently ground according to the invention.

Figure 12 is an enlarged longitudinal section through a tapered roller bearing cone or inner race showing the relationship between the hearing raceway, together with the tapered frustoconical rollers arranged therebetween.

General arrangement In general, the machine in connection with which this invention is used, consists of a grinding wheel having a novel configuration for substantially simultaneously or concurrently grinding the raceway, one side wall and one edge of an anti-friction bearing cone. The invention comprises truing mechanism for truing the face of the grinding wheel which grinds the raceway and also for truing the groove in the grinding wheel which simultaneously grinds the side wall and one edge of the bearing cone; and also includes the method of truing the grinding wheel in this manner.

Hitherto, anti-friction roller bearings have been provided with outer and inner races between which the bearing rollers have been arranged. Tapered roller bearings have been provided with a conical inner race or cone and an annular outer race coacting therewth.

In a tapered roller bearing of this type (Figure 12), the pressure exerted upon the outer hearing race is transmitted through the frusto-conical rollers and gives rise to an axial component of force which urges the ends of the rollers against one of the side walls of the inner bearing race or cone. The heat generated by the friction between the ends of these rollers and the side wall of the bearing race becomes concentrated at the edge of the side wall, with the result that the temper was frequently taken out of that portion of the bearing race and rapid wear enhanced.

Accordingly, after the inner bearing race had been completely ground, it has been customary to round oi! the edge of the side wall which receives the thrust of the ends of the rollers, so that this heat is not concentrated but is distributed throughout that portion of the bearing race. This rounding of the edge has hitherto necessitated a separate and costly operation in the grinding of the bearing race or cone and has also resulted in inaccuracies of manufacture.

According to the present invention. however, a machine and method of truing the grinding wheel are provided whereby the race-way, side wall and adjacent edge of the inner bearing race or cone are ground substantially or concurrently, thereby eliminating this additional operation. To accomplish this, the grinding wheel which grinds the inner raceway is trued with a groove of predetermined coniiguration in such a manner that the face of the grinding wheel grinds the inner raceway of the bearing cone, whereas one wall of the groove grinds the side wall of the bearing race while the other wall of the groove rounds the edge adjacent the side wall.

Work support construction The mechanism for supporting the work piece, namely, the inner cone of bearing race, is disposed in the lower left-hand corner of Figure 1. The entire machine is mounted upon a suitable pedestal (not shown) supporting a base In having v-ways II for slidably supporting a carriage I2 having corresponding V-ways I3 cooperating with the V-ways II (Figures 1 and 3).

The carriage I2 is provided with a threaded nut I4 secured thereto and receiving a screw shaft I5 rotatably mounted in a bearing boss I5 upon the base It and having on opposite sides thereof a collar-like enlargement I1 and a hand crank I8 secured as at I9 to the screw shaft I5. By operating the hand crank I8 in one direction, the carriage I2 may be moved inward, whereas by operating it in the opposite direction, the carriage l2 may be moved outward by means of the coaction of the screw shaft I5 and nut I4. The inward travel of the carriage I2 is limited by a stop screw 25 (Figure I) mounted in a threaded boss 2I at the opposite end of the ways II from the boss I5. A lock nut 22 upon the stop screw 20 securely anchors the latter in its adjusted position. By this means, the carriage I2 may be advanced only so far as the end of the stop screw 20, which accordingly determines in part the adjustment of the work piece relatively to the grinding-wheel, as hereinafter set forth in more detail.

The carriage I2 is provided with transverse V-ways 23 co-acting with corresponding V-ways 24 upon a cross slide 25 having a threaded nut 25 secured thereto or integral therewith (Figure 3). The nut 26 receives a screw shaft 21 rotatably supported in a boss 28 upon the carriage I2 and having on its opposite sides an enlargement 29 and a hand crank 30 secured to the screw shaft 21. By turning the hand crank 30, the cross slide 25 may be moved to and fro across the carriage l2 in order to assist further in positioning the work piece or bearing cone relatively to the grinding-wheel.

The cross slide 25 is provided with a central vertical bore 3| adapted to receive a pivot screw 92 passing through a vertical bore 33 in the swivel member 34 and terminating in a retaining nut 35 and washer 35 (Figure 3). The cross slide 25 is provided with a cylindrical depression I! co-acting with a cylindrical projection 38 upon the underside of the swivel head 34 and co-axial tional support for the swivel movement of the swivel head 34.

The swivel head 34 is provided with bores 39 (Figures 1 and 3) rotatably supporting a tubular shaft 45 having on its forward end a flange 4i provided with a socket 42 for receiving the workholding chuck 49.

The chuck 49 is provided with converging bores 44, three such bores being shown. These bores 44 reciprocably support the work-holding pins 45 having enlarged offset ends 45 urged forward by coil springs 41 (Figure 1). Near their forward ends the pins 45 are provided with oblique notches 48 having side walls 49 (Figure 11) and end walls 55. The side walls and end walls 49 and 50 serve respectively to engage the inner bore 5I and end surface 52 of the inner bearing race or cone 52 which constitutes the work piece. The latter is also provided support by an annular abutment 54 on the end of the chuck 43.

As hereinafter explained (Figure 11), the hearing cone 53 is also provided with a conical raceway 55 for the frusto-conical bearing rollers 55 (Figures 11 and 12) terminating in annular grooves 51 and 58 from which arise the end flanges 59 and 60 having end walls 5| and 62 respectively. The end wall 5| co-acts with the end wall 53 of the tapered roller 55, the latter being urged thereagainst by the forces exerted upon the outer bearing race or ring 54 having an inner conical surface 55 engaging the frustoconical roller surface 65. The smaller end 61 of the bearing roller 56 is urged away from the side wall 62 (Figure 12) by the same forces which exert components in the direction of the axes of the rollers 66 toward their larger ends 63. The edge 68 of the end wall 6| on the flange 59 is rounded so as to prevent the concentration of the heat at this edge, this heat resulting from the friction generated between the roller ends 63 in the side wall 5 I.

The work holding pins 45 are normally held in a retracted position by the engagement of a head 59 upon a shaft 15 (Figure 1) passing through a bore II in the tubular shaft 45. The latter is held in position by a pair of retaining rings I2 and 13 threaded upon the rearward ends thereof and engaging a circular boss 14 on the rearward side of the swivel head 34 (Figure 1). The tubular shaft 46 also carries a pulley I5 by which the shaft 40 may be rotated. This is preferably accomplished'by a belt driven from a motor (not shown) preferably mounted on top of the swivel head 34. This motor and belt have been omitted in order to prevent obstructing the parts located beneath them.

On the shaft I0 at its rearward end is mounted a flanged collar I6 secured thereto by the bolt TI. A coil spring 18 disposed between the end of the tubular shaft 40 and the flanged collar I5 urges the latter and its shaft I0 rearwardly, holding the work-holding pins 45 in a retracted position by reason of the engagement of the shaft head 69 with the offset projections 46 on the pins 45. The shaft I0 adjacent the pins 45 is reciprocably supported in a bore I9 within the chuck 43. When the pins 45 are in their retracted positions, the walls 49 of the notches 48 engage the inner bore 5| of the bearing cone 53 and urge it rearwardly against the abutment 54 (Figure 11), holding the bearing cone 53 or work piece securely against this abutment while at the same time accurately centering the work piece.

In order to advance the work holding pins 45 and withdraw their surfaces 49 from engagement with the inner bore 5I of the bearing cone 53, thereby releasing the work piece, the shaft I and its head 69 are moved forwardly, thereby permitting the coil springs 41 to so advance the pins 45. This is accomplished by means of .a yoke 80 having a forced end 8| engaging the grooved collar 16 and secured as at 82 upon the rod 83 (Figure 1). The rod 83 is reciprocably supported in a bore 84 within the swivel head 34 (Figures 1 and 3) and carries a projecting pin 85 having a beveled cam surface 86 upon the outer end thereof. This cam surface 86 is engaged by a pin 81 mounted upon the hand lever 88 which is pivotally mounted upon the pivot pin 89 supported in thebracket 90 extending horizontally outward from the swivel head 34 (Figure 1). Thus, by pushing the hand lever 88 inward toward the swivel head 34, the pin 85 is pushed forward by the engagement of the pin 81 with the cam surface 86, moving forward the rod 83, yoke 80, flanged collar I0, shaft I0 and head 69. The latter moves forward in the chuck chamber 9I, releasing the pins 45 so that they are urged forward by their coil springs 41, releasing the bearing cone or work piece 53. While the pins are in this advanced position, a new bearing cone may be placed in position, after which the hand lever 88 is released and the bearing cone simultaneously centered and chucked in a reverse manner to that previously described. When the hand lever 88 is released, the coil spring I8 pulls the pins 45 back into their chucking position under the urge of the shaft I0 and its head 89 engaging the offset portions 46 of the pins 45.

Grinding-wheel mechanism The right-hand portion of the base I0 is provided with V-ways 92 of the dovetail type and running entirely across the base I0. Slidably mounted upon the ways 92 is the grinder carriage 93 and carrying a rack 94 upon its underside (Figures 1 and 2). Meshing with the rack 94 is a pinion 95 mounted on a shaft 96 journaled in the base and carrying a hand lever 91 secured as at 98 to the outer end of the shaft 96. By reason of this construction, the carriage 93 may be reciprocated along the ways 92 merely by swinging the hand lever 91. The carriage 03 is provided with a projection 99 having a threaded bore I00 carrying a threaded stop screw I0! which is adapted to be locked in place by a lock nut I02. The stop screw IOI engages a stop projection I03 rising from the base I0 and serving to limit the forward motion of the carriage 93.

Mounted upon the carriage 93 is a motor I04 having a shaft I05 carrying a pulley I06 which is connected by the belt I01 to a pulley I08 upon the grinder shaft I09. The latter is journaled in the portion H0 of the carriage 93 and carries on its opposite end a huh I I I on which is mounted the grinding-wheel H2. The grindingwheel H2 is secured thereto by the cap screw H3 and Washer H4.

The grinding-wheel H2 is of a peculiar conby the bearing cone 53 which is to be ground. The angle between the raceway grinding surface H5 and the side wall grinding surface III may be degrees for certain bearing cones. In order to true these surfaces of the grinding-wheel I I2 to the proper angles and to maintain these angles and surfaces in the proper condition, it is necessary to provide grinding-wheel truing mechanism which is operable accurately for this purpose.

Grinding-wheel truing mechanism The grinding-wheel truing mechanism may be mounted in any convenient location where it is accessible to the periphery of the grindingwheel. For purposes of illustration, the arrangement has been shown in the drawings wherein the truing mechanism is brought into engagement with the front portion of the periphery of the grinding-wheel.

Mounted on the forward portions of the V- ways 92 is a truing carriage I20 having corresponding ways I2I. The carriage I20 carries a nut or boss I22 with a threaded bore I23 adapted to receive a screw shaft I24. The latter passes through a bore I25 in the bridge portion I26 of the base I0 and carries a hand crank I21 secured as at I28 to the outer end of the screw shaft I24 and which cooperates with a shaft enlargement I29 on the opposite side of the bridg I26 (Figure 1).

The truing carriage I02 is provided with cross ways I30 (Figures 1, 4 and 5) arranged at right angles to the ways 92, the apparent parallel showing of the ways 92 and I30 in Figures 4 and 5 being due to the fact that the section line 55 in Figure 1 outs obliquely across both of the Ways 92 and I30. Mounted on the cross ways I30 is a cross slide I3I having ways I32 cooperating with the ways I30. The truing cross slide I3I carries a nut or boss I33 (Figures 1 and 2) having a threaded bore I34 adapted to receive a screw shaft I35 journaled in the bridge portion I36 and carrying a hand crank I31 on its outer end. By means of the hand cranks I21 and I31, the truing carriage I20 and the truing cross slide I3I may be manipulated at right angles to one another in order to position the truing mechanism relatively to the grinding-wheel H2.

The truing cross slide I3I is provided with a central threaded bore I38 (Figure 5) serving to receive a pivot screw I39 having its upper end mounted in a bore I40 within the truing swivel I4I, the latter being provided with a cylindrical projection I42 rotatable within a cylindrical recess I53 in the truing cross slide I3I and coaxial with the pivot screw I38. The truing swivel I4! is provided with an arcuate slot I44 in a projecting portion I45 and having its center at the axis of the pivot screw I39. A clamping bolt I45a mounted in a threaded hole I48 serves to clamp the truing swivel I4I to the desired position to which it has been rotated.

Mounted upon the truing swivel I4I are the top slideways I 41 (Figure 5) upon which the top slide I48 is reciprocably mounted by means of its corresponding ways I 48a.

The top slide I88 is provided on its underside With a threaded boss or nut I53 having a threaded bore I5I receiving the screw shaft I52. The screw shaft I52 is journaled in the bore I53 within the bridge portion I54 and carries a hand crank I 55 on its outer end (Figure 1). By rotating the hand crank I55, the top slide I48 may be moved to and fro along the ways I41 on top of the trulng swivel I.

a reciprocable bar I51 having a corresponding groove I58 to flt the slideway I58. The bar I51 is provided with longitudinal slots I59 through which pass the clamping bolts I60 which are threaded into holes I 6| in the side of the head I49. The bar I51 i provided with a threaded longitudinal bore I62 (Figure 6). adapted to receive a screw shaft I83 Journaled as at I64 in a plate I65 secured to the head I49 and carrying a knurled head I66. Thus, by loosening the clamping bolts I60 and rotating the screw shaft I63, the bar I51 may be moved in or out as desired. The outer end of the bar I51 is provided with a bore I61 terminating in a socket I98 adapted to receive a trulng element I69 containing a trulng crystal I10 such as a diamond or other extremely hard substance (Figure 6). The trulng element I69 is held in position by a set screw I1I (Figure 7), and has for its purpose the trulng of the grinding-wheel portion II for grinding the raceway 55 of the bearing cone 53.

The head I49 is also provided with a longitudinal bore I12 (Figure 6) adapted to slidably receive a shaft I13 and provided with a keyway I14 containing a key I15 which enters a corresponding keyway; I16 in the shaft I13 to prevent rotation of the latter while it is being advanced or retracted. The shaft I13 is provided with an internal bore I11 adapted to receive a hollow nut I18 in the form of a threaded sleeve, which in turn receives a screw shaft I19. The screw shaft I19 is provided with an outer portion I80 journaled in a bore I8I within a cap I82 threaded as at I83 into a bore I84 concentric with the bores I12 and I11. Mounted as at I85 on the outer end of the screw shaft portion I80 is a hand crank I86 for rotating the screw shaft I19, and accordingly advancing or retracting the shaft I13.

rhe outer end of the shaft n3 is cut away as at I81 (Figure 6) and is provided with a slideway I88 (Figuresfi and '7). The latter is engaged by a corresponding groove I89 in the block I90. The latter is provided with an oblique bore or socket I9I for receiving the trulng element I92 containing a trulng crystal I93, such as a diamond or other extremely hard substance. The trulng element I92 is likewise anchored in position by means of a set screw I94 (Figure '1).

The end of the bar I13 is provided with a transverse bore I95 (Figure 6) having smooth walls and rotatably receiving the smooth shank of a cap screw I96, the threaded portion I91 of which passes through an enlarged hole I98 into an eccentric nut I99 having a smooth cylindrical outer surface 200 seated in a vertical groove 20I the axis of which is eccentric to the axis of the bore I95. By loosening the cap screw I96 and applying a wrench to the hexagonal portion 202 of the nut I99, the latter may be rotated in its groove 20I and the block I90 thereby moved to and fro along its slideway I88. When this adjustment has been performed as desired, the cap screw I96 is tightened so as to anchor the block I90 in its adjusted position.

The relative positions of the trulng elements I69 and I92 are shown in Figures 9 and 10. The tip of the trulng crystal I93 is rounded as at 203 (Figure 9) in order to create the rounded portion H8 in the grinding-wheel II2. This rounded portion I I8 in the groove I I 6 produces the rounded edge 68 on the bearing cone 63 at the same time that the side wall 6| is produced by the grinding-wheel portion II1 (Figures 9, 11 and 12) The trulng crystal I93 is also provided with approximately conical walls 204 for finishing the opposite wall of the groove II6 of the grindingwheel II2. In order to limit the forward motion of the shaft I13, the threaded sleeve I18 (Figure 6) is provided with a flanged head 205 which comes into engagement with the annular shoulder 206 when the shaft I13 is moved forward as far as it will go. This provides a means whereby the tips of the trulng diamonds or crystals I10 and I93 may be properly positioned relatively to each other as that the groove H6 and raceway grinding surface II5 of the grinding-wheel II2 may be formed to the proper dimensions and proportions.

Operation In the operation of the machine and the practicing of the method of the invention, the grinding-wheel II2 must first be formed to the desired configuration by the action of the trulng mechanism. For this purpose, the slides I2 and 25 and the swivel are manipulated to withdraw the work holding pins 45 from their grinding position (Figure 1) to their withdrawn position (Figure 2). The slides I20 and I3I, the swivel III, and the top slide I48 are then adjusted by turning their respective hand crank until the ways I41 of the top slide I49 are approximately parallel to the direction of the surface I I5 which is to be formed upon the grinding wheel II2. In the example shown (Figure 11), the direction of the surface H5 is approximately 45 degrees to the axis of the grinding wheel shaft I09, but other angles may be found suitable with different types of work piece. The swivel I4I is then clamped by tightening the cap screws I45.

The cap screws I60 are then loosened and the bar I51 moved by turning the knurled head I68 until the tip of the trulng diamond or crystal I10 is in the proper position. Meanwhile, the shaft I13 is adjusted by turning the hand crank I86 and also by loosening the cap screw I96 (Figure 6) and rotating the eccentric nut I99 until the trulng diamond or crystal I93 is positioned properly relatively to the trulng diamond or crystal I10. The flanged head 205 on the threaded sleeve I18 serves as a stop. to limit the inward motion of the shaft I 13 when it comes into engagement with the annular shoulder 206 at the end of the threaded bore I84. When this occurs, the tip of the trulng diamond I93 should be in advance of the tip of the trulng diamond I10 by substantially the depth of the side wall trulng portion II1 of the grinding-wheel II2. Thus the raceway grinding surface II5 may be trued and the groove II6 out immediately afterward by advancing the shaft I 13 until the flange 205 engages the annular abutment or shoulder 206 (Figure 6).

To form or true the raceway grinding surface II5, the shaft I13 is retracted (Figure 6) so that the trulng diamond I10 projects beyond the end of the block I90. The screw shaft I52 is then rotated by turning the hand crank I55, causing the trulng diamond I10 to pass over the peripheral surface of the grinding wheel II2 (Figure 10), forming or trulng the surface II5. It is, of course, understood that after the surface I I5 is originally formed, it can be used only a limited time before it requires re-truing.' The head I49 is then retracted by rotating the hand crank I55 in the opposite direction. The raceway grinding surface is then in its completed condition.

To form the groove I I8 in the periphery of; the grinding wheel H2, the hand crank I86 is then turned until the truing diamond l 93 puts its way into the periphery of the grinding wheel H2 (Figure 9), coming to a halt when the stop flange 285engages the stop shoulder or abutment 208. As this occurs, the side wall grinding surface H1 is first formed, and the rounded portion 8 subsequently formed (Figure 9) by the rounded top .288 of the truing diamond 204 as the latter reaches the end of its travel. During this operation, the truing mechanism occupies the position shown in Figure 2. The machine is then ready for its grinding operations.

To grind a. bearing race 53, the hand lever is Thus, the invention provides a machine and method whereby a grinding wheel may be trued swung inward (Figure 1) pushing the shaft 18 and its head 69 forward, permitting the work holding pins 45 to advance under the urge of the coil springs 41. A work piece on bearing cone 83 is then pushed into place over the pins 45 and the hand lever 88 released. The spring 18 then pulls the shaft 18 and head 69 backward, retracting the pins 45 and causing their surfaces 49 to tightly engage and center the inner b'ore SI of the bearing race 53.

Meanwhile, the work-holding pins 45 have been brought into the proper relationship to the grinding-wheel H2 by manipulating the hand cranks l8 and 30 and swinging the swivel head 34, thus moving the parts from the truing position (Figure 2) to the grinding position (Figure 1). The motor I84 is then started and the grinding-wheel I I 2 rotated.

As the grinding-wheel H2 rotates, the portion 8 thereof grinds the raceway surface 55 while the portion ll'l grinds the side wall 6| and the rounded portion H8 rounds off the edge 68. In this manner, the principal surfaces on the periphery of the bearing cone 53 are simultaneously or substantially simultaneously ground, thereby reducing the grinding operations to a minimum and eliminating separate operations,

When the grinding has been completed, the pins 48 are again retracted by swinging the hand lever 88 inward, whereupon the work piece may be removed and a new work piece inserted. The latter becomes centered and clamped in position when the hand lever 88 is released. These operations may be repeated indefinitely until the order has been completed or the grinding wheel 2 requires retrulng.

,to simultaneously grind a raceway and a side wall, and at the same time round the edge of the latter.

The side wall 6! of the bearing cone 53 is disposed at approximately degrees to the bearing raceway 53. The frusto-conica-l' rollers 56 have a lesser angle between their sides and larger end, but this is compensated for by rounding the larger end of the roller 56, preferably to a spherical or approximately conical shape.

As previously stated, the thrust of the outer race 64 upon the bearing rollers 56"tends to urge the ends 63 thereof against the side wall 6|, producing heat which becomes concentrated at the edge of the side wall 6|. The rounding of this edge 68, however, reduces this concentration of heat, and reduces the noise of the bearing, so that a more silent bearing is obtained.

While a specific embodiment of the invention has been described and illustrated, it will be understood that various modifications may be made within the scope of the appended claims without departing from the spirit of the invention.

What I claim is:

1. An adjustable cutter unit comprising a holder having a guideway, a cutter carrier slidable along said guideway and having an arcuate recess therein, a bolt supported by said holder and extending transversely to said carrier and projecting into said recess, a cutter adjuster nut having an eccentric boss rotatably mounted on said bolt and having an eccentric portion engaging said recess, and said nut and bolt serving for selectively and releasably clamping said carrier to said member.

2. An adjustable cutter unit comprising a holder having a guideway, a cutter carrier slidable along said guideway and having an arcuate recess therein and an elongated aperture extending therethrough from said recess, a bolt supported by said holder transversely to said carrier and extending through said aperture into said recess, a rotary cutter adjuster rotatably mounted on said bolt and having an arcuate portion eccentric to said bolt engaging said recess and a nut having an eccentric boss engaging within said arcuate recess for selectively and adjustably clamping said carrier to said holder.

GLEN F. JOHNSON. 

